1. Field of the Invention
The present invention relates to a bottle for containing a drink, particularly a drink not containing a carbonic acid gas, such as juice or tea, which bottle is formed by blow-molding synthetic resin, and is provided with a special closure.
2. Description of the Related Arts
Recently, most bottles for containing a drink such as juice or tea not containing carbonic acid gas are made of polyethylene terephthalate (PET) resin, by a blow-molding process, because PET is relatively low cost and has a good mechanical durability. One example of the production methods thereof is disclosed in Japanese Examined Patent Publication (Kokoku) No. 62-5781. According to this publication, a preform in a shape of test tube made of the above resin is put into a mold having a cavity corresponding to a contour of the required bottle while the preform is heated above a glass transition point of the resin. Then air is blown into the interior of the preform through a mouth thereof to expand the preform within the cavity. The air blowing is continued until the expanded preform is in contact with the inner wall of the mold, for a predetermined period, and the mold is maintained at a temperature above a crystallizing temperature of the resin so that interior stress in the expanded preform is relaxed. Finally, a PET bottle thus formed and having a narrow neck and a bi-axially oriented wide body as shown in FIG. 1, is removed from the mold.
When a drink such as juice is contained in this bottle, the juice is heated at a temperature of from 65.degree. C. to 95.degree. C. and poured therein, a closure is fitted on a neck of the bottle, and the bottle is laid horizontally so that the content therein reaches the inside of the neck to sterilize the closure and the entire interior of the bottle.
A roll-on closure-made of aluminum sheet is usually fitted to the bottle, and this capping is carried out in the following manner. A blank closure without a thread is fitted onto the bottle neck, around which a thread was formed during the molding process. The blank subjected to an axial load of more than 200 kg.wt, and at the same time, a disc is applied to the side wall of the blank closure in such a manner that a narrow edge of the disc presses the side wall into a thread groove on the bottle neck, and thus a thread corresponding to that on the bottle neck is formed on the closure and a tight capping is achieved.
As a result, a side wall of the bottle neck is always under an inward stress after capping, and the top surface of the bottle neck is under a downward stress.
It should be noted that the bottle neck has a lower softening point relative to the bottle body because the bottle neck has not been expanded and oriented during the molding process. Therefore, when the hot juice reaches the bottle neck and heats the same for sterilization, the temperature of the bottle neck is elevated above a glass transition point of the resin. Accordingly, the bottle neck is softened, and thus is deformed by the prestress caused by the closure, and therefore, the sealing effect of the closure is greatly reduced.
To eliminate this drawback, prior to the molding of the bottle body, the bottle neck is subjected to a heat treatment separately from the bottle body. In this special heat treatment, the bottle neck is crystallized to have a higher softening point, as disclosed in Japanese Examined Patent Publication (Kokoku) No. 61-35056.
This proposal, however, requires an additional device for heating the bottle neck alone, and a means for precisely controlling a dimensional change of the bottle neck during the heat treatment so that a closure is tightly fitted thereon, which causes technical difficulties, and further, raises the manufacturing cost. In addition, the crystallized bottle neck is made opaque, and does not match the transparent body.